There's also much more recent research where you can actually track the position of people by the changes to the Wifi signal. Passive monitoring only, no device involved. See https://github.com/Saad-Imtiaz/WiFi-Sense for example (first thing I found by looking up now, never tried myself).

You could look for Bluetooth MACs instead but those too are randomized. Are any other vendors randomizing Bluetooth MACs? Maybe that's what they detect, MACs that don't go to any known vendor.

For years starting in the late teens and fizzling out over covid university paper after university paper about "this is so cool look how we can see through walls by essentially using 5g and wifi as ambient light" and they steadily marched up the chain from simple room layouts to furniture layouts, occupant detection, occupant movement and then started being dressed up with the usual dogwhistle language about "emergency services" that people who are building tech to help infantry/police entry teams use to make it seem more noble and then after that it all just kinda stopped being publicized with any sort of regularity?

To me that says that the tech got good enough all those people got hired to make it production worthy behind closed doors.